Lightning rods and Corona Discharge

[Stephen Bulking]

1) Q: Why does lightning strike high and sharp targets like a lightning rod?
A: Assuming that there is a massive collection of charge, possibly in clouds of a thunderstorm, trying to get to the ground where there is a pool of the opposite charge through an insulator that is air. I believe this is impossible until the accumulated charge in the clouds grow large enough to produce a electric field that overpower the dielectric strength of air and when it does, the necessary condition for a lightning bolt to occur is met. The preferred being installed at the top of the building feature of a lightning rod is actually there to shorten the distance between "heaven" and Earth, same reason why lightning prefers to strike trees. As for the sharp feature, in the embedded material I have included a very detailed explanation as to why sharp objects "charged" to a smaller potential would still efficiently produce a strong electric field as would larger objects, thus facilitating an "environment" through which accumulated charges in the clouds can easily move down on the rod then to the Earth. This along with the aforementioned reason why lightning tends to strike down on tall objects are my answers to this question.
2) Q: As written in the material, to prevent Corona Discharge the OTHER end of the LIGHTNING ROD is preferably BLUNT. Why? By OTHER end, is the other end conventionally sharp? (silly question but I don't trust my own answer so...)
A: So as to store up more charges without breaking the dielectric strength of air, yeah maybe idk bruh...
References:

 

[hutchphd]

The other end is buried in the Earth or any other handy high capacity conductor, so I do not understand the question .

 

[Stephen Bulking]

The other end is buried in the Earth or any other handy high capacity conductor, so I do not understand the question .

Well in the pictures taken from my book that I posted along with this thread, it says that: "A large-radius conductor is used in situations where it’s important to prevent corona. An example is the blunt end of a metal lightning rod. A lightning rod with a sharp end would allow less charge buildup and hence would be less effective." But we always see sharp spearhead lightning rods pointing up towards the sky in real life so where is the blunt end? And according to my video I don't think we necessarily bury one end into the ground, we do ground it though by means of maybe a cable a a large copper stick...?

 

[Lnewqban]

I have found this for you:

https://en.m.wikipedia.org/wiki/Lightning_rod

“Rounded versus pointed ends

The optimal shape for the tip of a lightning rod has been controversial since the 18th century. During the period of political confrontation between Britain and its American colonies, British scientists maintained that a lightning rod should have a ball on its end, while American scientists maintained that there should be a point. As of 2003, the controversy had not been completely resolved. It is difficult to resolve the controversy because proper controlled experiments are nearly impossible, but work performed by Charles B. Moore, et al., in 2000 has shed some light on the issue, finding that moderately rounded or blunt-tipped lightning rods act as marginally better strike receptors. As a result, round-tipped rods are installed on most new systems in the United States, though most existing systems still have pointed rods. According to the study,

Calculations of the relative strengths of the electric fields above similarly exposed sharp and blunt rods show that while the fields are much stronger at the tip of a sharp rod prior to any emissions, they decrease more rapidly with distance. As a result, at a few centimeters above the tip of a 20-mm-diameter blunt rod, the strength of the field is greater than over an otherwise similar, sharper rod of the same height. Since the field strength at the tip of a sharpened rod tends to be limited by the easy formation of ions in the surrounding air, the field strengths over blunt rods can be much stronger than those at distances greater than 1 cm over sharper ones.
The results of this study suggest that moderately blunt metal rods (with tip height to tip radius of curvature ratios of about 680:1) are better lightning strike receptors than sharper rods or very blunt ones.”

 

[hutchphd]

So perhaps God's eyesight is not what it once was? Should we perhaps paint the tips with hunter orange or reflectors...
Very interesting actually.

 

[davenn]

And according to my video I don't think we necessarily bury one end into the ground, we do ground it though by means of maybe a cable a a large copper stick...?

It IS necessary, and it is ALWAYS done with lightning rods. In a past life in the telecommunications industry, I was involved with the installation of radio towers and the assoc. installation of lightning protection.

The very large earthmat we installed in the ground and buried often covered 10 to 20m²
This to produce as low an impedance as possible connection between the lightning rod and its conductor to the ground


Dave

 

[anorlunda]

British scientists maintained that a lightning rod should have a ball on its end, while American scientists maintained that there should be a point.

Maybe that's why some have both ball and points. They cover both bases. The variations in design seem endless.

Boats with non-metallic hulls, need to settle for less. This dnyaplate is a commonly used way to ground the lightning rod in a boat.

Devices like the one below are called charge dissipators. Their usefulness is similarly disputed and controversial.

It seems likely that none of these controversies will be settled in our lifetimes.

 

[Lnewqban]

... Devices like the one below are called charge dissipators. Their usefulness is similarly disputed and controversial.

View attachment 269026

Very interesting, anorlunda!
That picture reminds me of airplanes having “static discharge wicks”, which work based on a similar principle.

Please, see:
https://en.m.wikipedia.org/wiki/Static_discharger

 

[Stephen Bulking]

I have found this for you:

https://en.m.wikipedia.org/wiki/Lightning_rod

“Rounded versus pointed ends
The optimal shape for the tip of a lightning rod has been controversial since the 18th century. During the period of political confrontation between Britain and its American colonies, British scientists maintained that a lightning rod should have a ball on its end, while American scientists maintained that there should be a point. As of 2003, the controversy had not been completely resolved. It is difficult to resolve the controversy because proper controlled experiments are nearly impossible, but work performed by Charles B. Moore, et al., in 2000 has shed some light on the issue, finding that moderately rounded or blunt-tipped lightning rods act as marginally better strike receptors. As a result, round-tipped rods are installed on most new systems in the United States, though most existing systems still have pointed rods. According to the study,

Calculations of the relative strengths of the electric fields above similarly exposed sharp and blunt rods show that while the fields are much stronger at the tip of a sharp rod prior to any emissions, they decrease more rapidly with distance. As a result, at a few centimeters above the tip of a 20-mm-diameter blunt rod, the strength of the field is greater than over an otherwise similar, sharper rod of the same height. Since the field strength at the tip of a sharpened rod tends to be limited by the easy formation of ions in the surrounding air, the field strengths over blunt rods can be much stronger than those at distances greater than 1 cm over sharper ones.
The results of this study suggest that moderately blunt metal rods (with tip height to tip radius of curvature ratios of about 680:1) are better lightning strike receptors than sharper rods or very blunt ones.”

Thank you for your quick response. I find your answer very relatable.

 

[Lnewqban]

Thank you for your quick response. I find your answer very relatable.

You are welcome.

 

[sophiecentaur]

Devices like the one below are called charge dissipators. Their usefulness is similarly disputed and controversial.

I would have thought that the usual sacrificial anode, made of Zinc and used to reduce electrolytic action on propellors and drive shafts, would achieve the same thing as long as the lightning rod is connected as well as the rest of the electrics and metal bits.